Why is your pool green?

Before we dive into (pun intended) the how of getting that pool back to blue, let’s take a look at why it turned green in the first place.

In most cases, a pool will become green because of an overgrowth of algae, but the causes for this overgrowth can vary.

The main ones are:

Improper PH balance. A pH level that's too low can erode pool materials and cause eye irritation, but too high and it will not kill bacteria or algae and can also cause skin irritation. A PH level that is out of balance in either direction can lead to issues with water discoloration (read: How to balance pool water).

Clogged filter. If your filter isn’t working (check out the best pool filters), you’re obviously going to have trouble keeping it clean. Not only will algae continue to grow, but you could also be breeding bacteria and debris that will discolor the water.

Change in weather. Algae thrives in warm, humid environments, so if you’ve recently experienced a change in your weather, you’ll need to be extra diligent about cleaning the pool.

Hopefully now you’ve pinned down the culprit of the discolored pool, so let’s get down to business!

It may seem like the end of the world (or at least the summer) when your pool turns into a slimy green mess, but rest-assured, pool owners, I’ve got you covered.

If you follow these six simple steps to cleaning your green pool fast, I’ll have you back on your floatie in clean water in no time.

1. Does it need to be drained?

If your pool is dark green, bordering on a blackish color, it may be more effective to drain the pool completely and acid wash the surface.

Rob at Dengarden says “if you can see at least six to eight inches below the surface of the water, most likely the pool can be treated chemically.”

If not, you will need to make your own decision about whether to drain the water or continue to try chemical treatments.

Most pool shock products give great instructions on how much to use for various situations, but Pool Spa News states that scientifically, to de-structure the DNA of algae, you need to chlorinate the water to 30 ppm (or 30 parts per million).

Use your testing kit to reach the right balance.

4. Pump & filter

Next, you’ll need to pump the water and filter it to regain balance. How you do this will depend on the type of filter you have.

If you have a DE or a sand filter, you’ll want to backwash the filter (aka clean your filter) before you do anything else in order to remove dirt and sediment.

Pool Center gives great directions here on how to do this, but the basic steps are:

1

Shut off pump, roll out backwash hose, check waste line for any closed valves.

2

Turn the multiport valve handle to backwash, or slide a push pull valve.

3

Turn on the pump. The water should flow out backwash pipe or hose.

4

Backwash until water runs clear, about 2-3 minutes.

5

Shut off pump, turn valve back to filter, turn filter back on.

6

Note lower pressure on filter tank, and increased flow rate.

5. Floc your pool

After this process, your pool will still probably be a little cloudy from leftover residue—specifically, a “high concentration of microscopic particles of dirt, bacteria or other substances that are resistant to pool chemicals and small enough to pass through filtration.” (source)

Adding a flocculent helps the debris clump together so that it can easily be vacuumed from the bottom of the pool, leaving you with crystal clear water.

6. Kill the algae

You’ve probably eliminated most of the algae in your pool by now and you may even feel that another step is just not necessary, but taking this one extra step could possibly keep you from having to repeat this entire process again in another week.

The thing is that algae grows very quickly and can take over your pool from just a few tiny spores. Killing it will drop it to the bottom of the pool floor.

Tips for maintaining your pool going forward

The easiest way to clean your pool is to maintain it well enough that algae and debris don’t get out of hand.

Here are a few simple things you can do to make sure your pool water stays crystal clear:

Check filters and pumps frequently. Algae thrives in stagnant water, so ensure that your filter and pump system is cleared of debris and working properly to keep the water moving and organisms skimmed off.

Brush and vacuum weekly. Scrub the surface and vacuum the bottom of the pool weekly to keep any dead algae or bacteria from growing.

Maintain a healthy PH level. It's recommended to test your pool’s PH levels 2-3 times a week along with your liquid chlorine (source). The recommended level to maintain is between 7.4 and 7.6. This level should stave off any algae spores before they have time to bloom.

Use a pool cover. Keeping out debris and other organisms that might blow in will help keep the yuck to a minimum. It will also keep the sun from supercharging any algae spores that are already lingering.

Bottom line

“An ounce of prevention is worth a pound of cure,” so they say, and that couldn’t be truer than it is with swimming pool maintenance.

A little extra TLC on your pool every week will keep you from having to muck out a dirty green mess once a month.